A telecommunications network, for example, the public switched telephone exchange (PSTN), enables the transfer of voice and data between terminals at geographically separated locations. One such network can be comprised of a series of nodes, each typically located in a city or other high traffic location, coupled together in a closed loop or ring architecture by fiber optic cables. The information travels along the fiber optic cables according to an optical transmission standard commonly known as either synchronous digital hierarchy (SDH) or synchronous optical networks (SONET). Ring architectures have long been preferred for such networks since they provide two separate paths for the flow of information between any two nodes of the ring.
In a fiber optic network which utilizes a four fiber ring architecture, traffic between adjacent nodes is normally carried on a first optical fiber commonly referred to as a working line. The nodes are also coupled together by a second optical fiber commonly known as a protect line. The diverse protect lines are use to restore the flow of information through the network during a failure or break in the lines which couple adjacent nodes of the network. Specifically, when the lines which couple adjacent nodes break, switching technology within the network nodes will re-route traffic between the nodes along an alternate path using the protect lines to circumvent the cable failure, thereby avoiding network outage.
Most networks are configured in a multi-ring architecture. In such networks, more than one ring will share a common node. Other multi-ring networks include overlapping ring sections, which result when a pair of rings share two or more adjacent nodes. If information transfers between the rings are possible, for example, at either of the common nodes, the overlapping ring section is said to be interconnected. A conventionally configured overlapping ring section with two rings, which is interconnected at both of the shared nodes, uses two bidirectional working lines and two bidirectional protect lines to couple the nodes. Of these lines, however, one working and one protect are dedicated to each one of the pair of rings. Accordingly, if a break occurs in one of the rings and the network re-routes traffic through the overlapping section thereof, the re-routed traffic will use the protect line dedicated to that ring. Consequently, one protect line in the overlapping ring section is redundant and not used.
Therefore what is needed is a method and an apparatus to eliminate redundant protect lines in an overlapping or on an inter-connecting route amount rings, thereby achieving tremendous savings in equipment and fiber costs, which does not sacrifice the quality of service or network capacity and survivability.